YouTube playlist verification v2 — fresh player per candidate, anti-leak assertion

v1 of this harness reused one player and called loadPlaylist(), which leaked the previous candidate's video and produced 14/15 false passes. v2 destroys and rebuilds the player for every ID, and asserts getPlaylist()[0] === the loaded video_id — if a stale video is still mounted, that check fails loudly.

Run the checks ~2 minutes · loads each playlist in a real embed, one at a time